Resistance weight training is often used for sports training and muscle development. For example, many athletes use free weights or weight training machines to improve muscle strength and endurance. Using free weights or weight training machines, while improving the muscles in general, does not necessarily improve the muscles used in particular sports motions, such as swinging a golf club.
Additionally, U.S. Pat. No. 6,599,201 describes a weight training apparatus that clamps to a shaft of a golf club.
U.S. Pat. No. 6,692,386 describes a baseball bat with a hollow cavity in which weights can be inserted.
U.S. Pat. No. 8,444,500 describes a flexible, crescent-shaped, weighted tube that can be slipped onto the shaft of golf club or baseball bat, or on the end of a tennis racket.